The present invention relates to a novel water-based metallic coating composition capable of forming a coating film which is excellent in a flip-flop property and which has no metallic mottling.
A water-based metallic coating composition prepared by mixing and dispersing a resin for a water-based metallic coating composition and a metallic pigment in water has already been known and is used as an top coating composition for an automobile outside plate. This coating composition is suited in terms of resource saving and public pollution control measure. However, there are the defects that a coating film formed has no satisfactory flip-flop property and that it is liable to bring about metallic mottling. Such defects are fatal for an top coating composition for an automobile outside plate, and a water-based metallic coating composition having no such defects is strongly desired to be developed.
An object of the present invention is to solve such defects as described above, which are involved in conventional water-based metallic coating composition, that is, to provide a water-based metallic coating composition capable of forming a coating film which is excellent in a flip-flop property and which is free of metallic mottling.
Intensive researches repeated by the present inventors have resulted in finding that the object described above can be achieved by further blending metal silicate and a polyamide resin with a water-based metallic coating composition comprising a resin composition for a water-based coating composition and a metallic pigment, and they have come to complete the present invention.
Thus, provided according to the present invention is a water-based metallic coating composition (hereinafter referred to as xe2x80x9cpresent coating compositionxe2x80x9d) comprising a resin composition for a water-based coating composition, a metallic pigment, metal silicate and a polyamide resin.
The present coating composition shall more specifically be explained below.
Resin Composition for a Water-based Coating Composition:
In general, the resin composition for a water-based coating composition used for the present coating composition comprises a conventionally known resin for a coating composition which can be dissolved or dispersed in water and a cross-linking agent. The above resin for a coating composition includes, for example, at least one base resin selected from an acryl resin, a vinyl resin, a polyester resin and a urethane resin each having a hydrophilic group such as a carboxyl group and a cross-linkable functional group such as a hydroxyl group together in a molecule. Suited as the above cross-linking agent is a hydrophobic or hydrophilic alkyl-etherified melamine resin which reacts with the cross-linkable functional group contained in the above base resin. In general, a proportion of the base resin to the cross-linking agent falls preferably in a range of 50 to 90% by weight, particularly 65 to 85% by weight in the case of the base resin and 50 to 10% by weight, particularly 35 to 15% by weight in the case of the cross-linking agent each based on the total amount of both components.
Metallic Pigment:
Capable of being used as the metallic pigment are flaky pigments which can provide a coating film formed from the present coating composition with a glittering brilliant feeling and a light iridescentry, and it includes, for example, flaky aluminum, deposited aluminum, aluminum oxide, bismuth oxychloride (for example, brand names xe2x80x9cMearlite Radiant Pearl STLxe2x80x9d, xe2x80x9cMearlite Radiant Pearl SUQxe2x80x9d and xe2x80x9cBBTxe2x80x9d (temporary name) manufactured by Engelhard Asia Pacific Inc.), mica, titanium oxide-coated mica, iron oxide-coated mica and micaceous iron oxide. These metallic pigments have preferably a dimension falling usually in a range of 1 to 30 xcexcm in a longitudinal direction and a thickness falling in a range of 0.001 to 1 xcexcm. In general, a blending proportion of the metallic pigment in the present coating composition falls suitably in a range of 0.5 to 40 parts by weight, particularly 3 to 25 parts by weight per 100 parts by weight (solid content) of the resin composition for the water-based coating composition.
Metal Silicate:
The metal silicate blended with the water-based metallic coating composition according to the present invention is suitably, for example, lithium magnesium sodium silicate (Si8((Mg5.34Li0.66)O20(OH)4)Na0.66), and a commercial product thereof includes, for example, a brand name xe2x80x9cLaponite RDxe2x80x9d manufactured by Laport Absorbents Co., Ltd. In general, a blending proportion of the metal silicate in the present coating composition falls suitably in a range of 0.5 to 5 parts by weight, particularly 1 to 3 parts by weight per 100 parts by weight (solid content) of the resin composition for the water-based coating composition.
Polyamide Resin:
The polyamide resin blended with the water-based metallic coating composition according to the present invention is suitably a waxy substance having such a relatively low molecular weight as an average molecular weight of 500 to 5000 and includes, for example, fatty acid polyamide waxes. A commercial product corresponding thereto includes, for example, a brand name xe2x80x9cDisparlon AQ-600xe2x80x9d manufactured by Kusumoto Chemicals Ltd. In general, a blending proportion of the polyamide resin in the present coating composition falls suitably in a range of 0.1 to 8 parts by weight, particularly 1 to 5 parts by weight per 100 parts by weight (solid content) of the resin composition for the water-based coating composition.
Other Additives:
An acid group (for example, a carboxyl group)-containing resin such as an acryl resin and a polyester resin each having a high acid value can be blended, if necessary, with the present coating composition. The above acid group-containing resin is preferably a resin having an acid value falling in a range of usually 10 to 200 mg KOH/g, particularly 30 to 120 mg KOH/g and a number average molecular weight falling in a range of 20000 to 120000, particularly 30000 to 80000. In general, a blending proportion thereof falls suitably in a range of 0 to 5 parts by weight, particularly 0.5 to 4 parts by weight per 100 parts by weight (solid content) of the resin composition for the water-based coating composition.
A phosphoric acid-containing resin, a settling preventive, a solid color pigment and an electrostatic aid can suitably added, if necessary, to the present coating composition.
Present Coating Composition and Coating Thereof:
The present coating composition can be prepared by mixing and dispersing the respective coating composition components described above in a water-based medium (for example, deionized water) by a conventional method.
The present coating composition is preferably coated on articles to be coated such as metal-made or plastic-made outside plate parts of passenger cars, auto trucks, auto-bicycles and buses and metal-made or plastic-made outside plate parts of household electric products directly or after coating in advance an undercoating composition such as a cationically electrodepositable coating composition and, if necessary, an intermediate coating composition on these articles to be coated and then curing these coating films. Metallic articles to be coated are preferably subjected in advance to chemical conversion treatment with phosphates and chromates. Further, conventionally known ones can be used as the undercoating composition and the intermediate coating composition.
The present coating composition can be coated on these articles to be coated (including those coated with the undercoating composition and further coated with suitably with the intermediate coating composition) by electrostatic coating, air spraying and airless spraying. A coating film thickness thereof falls suitably in a range of usually 5 to 30 xcexcm, particularly 10 to 20 xcexcm as a cured coating film. The coating film can be cured by heating at about 100 to about 180xc2x0 C. for about 10 to about 40 minutes.
In the coating film formed from the present coating composition, the metallic pigments are aligned evenly on a coated surface and parallel to the coated surface, and the coating film is excellent in a flip-flop (FF) property as compared with a conventional metallic coating film. In addition thereto provided is the marked effect that the metallic pigments are evenly dispersed and metallic mottling is scarcely observed.
A clear coating composition can be coated on the coating film of the present coating composition after curing it or without curing, that is, on a coated face thereof by a 2 coat 1 bake (2C1B) method or a 2 coat 2 bake (2C2B) method.
The clear coating composition is preferably a thermosetting coating composition which forms a colorless transparent or colored transparent coating film and includes, to be specific, a coating composition which contains a thermosetting resin composition and an organic solvent and which is blended, if necessary, with a solid color pigment, a metallic pigment and a UV absorber.
The thermosetting resin composition includes, for example, a composition comprising a base resin such as an acryl resin, a polyester resin, an alkyd resin, a fluororesin, a urethane resin and a silicon-containing resin each having a cross-linkable functional group such as a hydroxyl group, a carboxyl group, a silanol group and an epoxy group and a cross-linking agent such as a melamine resin, a urea resin, a (blocked) polyisocyanate compound, an epoxy compound or resin, a carboxyl group-containing compound or resin, an acid anhydride and an alkoxysilane group-containing compound or resin each capable of reacting with the above cross-linkable functional group. In general, a proportion of the base resin to the cross-linking agent falls preferably in a range of 50 to 90%, particularly 65 to 80% in the case of the base resin and 50 to 10%, particularly 35 to 20% in the case of the cross-linking agent each based on the total solid content weight of these both components.
Among these thermosetting resin compositions, preferably used is a composition capable of forming a coating film which is excellent in an acid resistance and a scratching resistance, comprising an acryl resin (base resin) having a cross-linkable functional group such as a carboxyl group, a silanol group and an epoxy group and a cross-linking agent selected from an epoxy compound or resin, a carboxyl group-containing compound or resin and an acid anhydride.
The clear coating composition can be coated by coating first the present coating composition on an article to be coated in the manner described above and then coating the clear coating composition having a solid content controlled to about 30 to about 80% by weight in coating on a coated surface thereof by electrostatic coating, air spraying and airless spraying after curing a coating film thereof by heating or as leaving it uncured. A film thickness of the clear coating composition falls suitably in a range of usually 5 to 100 xcexcm, particularly 20 to 80 xcexcm based on a cured coating film. The coating film can be cured by heating at about 100 to about 180xc2x0 C. for about 10 to about 40 minutes.
The present invention shall be more specifically be explained below with reference to examples and comparative examples. Both parts and percentage are based on weight, and a thickness of the coating film is based on a cured coating film.